Update the minimum required Remoting version to 3.14 (#4208)

* Let remoting handle missing channels

* Bump minimum remoting version to 3.14

core/src/main/java/hudson/Launcher.java

@@ -1327,11 +1327,7 @@ public abstract class Launcher {
                         Channel taskChannel = null;
                         try {
                             // Sync IO will fail automatically if the channel is being closed, no need to use getOpenChannelOrFail()
-                            // TODOL Replace by Channel#currentOrFail() when Remoting version allows
-                            taskChannel = Channel.current();
-                            if (taskChannel == null) {
-                                throw new IOException("No Remoting channel associated with this thread");
-                            }
+                            taskChannel = Channel.currentOrFail();
                             taskChannel.syncIO();
                         } catch (Throwable t) {
                             // this includes a failure to sync, agent.jar too old, etc

pom.xml

@@ -105,7 +105,7 @@ THE SOFTWARE.
     <!-- Bundled Remoting version -->
     <remoting.version>3.35</remoting.version>
     <!-- Minimum Remoting version, which is tested for API compatibility -->
-    <remoting.minimum.supported.version>3.4</remoting.minimum.supported.version>
+    <remoting.minimum.supported.version>3.14</remoting.minimum.supported.version>
 
     <!-- TODO: JENKINS-36716 - Switch to Medium once FindBugs is cleaned up, 430 issues on Mar 10, 2018 -->
     <findbugs.effort>Max</findbugs.effort>